Abstract: A nuclear logging-while-drilling measuring systems, and the correction of the formation property measurements for adverse effects of instrument standoff from the borehole wall, is disclosed. Detector responses for one or more downhole detectors are sampled and recorded over a time segment. The response samples are then sorted by magnitude, and a running integral of the sorted samples as a function of time is performed over the time segment. Linear segments are then fitted to the running integral, wherein each straight line segment is a function of one or more formation properties, and also a function of the standoff distance of the detector from the borehole wall. Segments are then combined to obtain a measure of one or more formation properties of interest such as formation density, where the adverse effects of borehole standoff are minimized. Standoff magnitude is also obtained and can be used to correct other logs, such as a neutron porosity log, for adverse effects of tool standoff and borehole size.

Abstract: A method of measuring characteristics of a geologic formation, using the time, energy and spatial spectra of gamma rays induced by an accelerator, which allows (i) the measurement of the photoelectric absorption (Pe) factor of the formation using a gamma-ray spectrum detected from gamma rays induced in the formation, (ii) the calculation of a neutron porosity of the formation using the gamma-ray spectrum, and (iii) the determination of a bulk density of the formation using the spectroscopic measurements. The Pe factor may be inferred by directly mapping the spectroscopic measurements. The porosity may be calculated by relating the gamma-ray spectrum to a hydrogen content of the formation. The density may be determined by computing a gamma diffusion length of the formation based on the gamma-ray spectrum. In addition to these measurements, the resistivity of the formation and its spontaneous potential may also be measured using an electromagnetic induction system.

Abstract: A well logging tool has a neutron source for irradiating formation surrounding a borehole. Two detectors are mounted in a spaced-apart vertical relationship within the tool pressure-resistant housing. Each detector detects capture gamma radiation across the entire gamma ray energy spectrum, windows are set in this spectrum to separate two distinct energy ranges, thereby generating a total of four independent sets of signals, two for each detector. One set of signals is indicative of the hydrogen content and insensitive to the chlorine content of the irradiated formation. The second set of signals is indicative of the hydrogen plus the chlorine content of the irradiated formation. By comparing the sets of signals in two proportional energy ranges, the logging tool allows to generate a log that helps determine the presence or absence of hydrocarbon or salt water in the formation.

Abstract: A well logging device of compact reduced diameter compared to the prior art, such well logging device having both short spaced and long spaced types of gamma ray crystal detectors installed in a measurements skid that comprises a relatively small diameter device constructed to withstand high temperatures and pressures, this device comprising a continuous stainless steel tube which provides pressure resistance and also allows low energy gamma ray transparency via large and small windows. This elongate type of stainless steel skid tube is furthermore internally supported by an internal tungsten tube placed therewithin, while the skid design also includes means for pressing the skid tube against a borehole wall so as to obtain more accurate formation density measurements downhole.